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  <div class="section" id="ufuncs">
<h1>Ufuncs</h1>
<p>Ufuncs or universal functions operate on ndarrays element by element, and support array broadcasting, type casting, and other features.</p>
<p>Lets try and see how we can use the binary and unary ufunc methods</p>
<p>After the neccessary includes</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="cp">#include</span> <span class="cpf">&lt;boost/python/numpy.hpp&gt;</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">&lt;iostream&gt;</span><span class="cp"></span>

<span class="k">namespace</span> <span class="n">p</span> <span class="o">=</span> <span class="n">boost</span><span class="o">::</span><span class="n">python</span><span class="p">;</span>
<span class="k">namespace</span> <span class="n">np</span> <span class="o">=</span> <span class="n">boost</span><span class="o">::</span><span class="n">python</span><span class="o">::</span><span class="n">numpy</span><span class="p">;</span>
</pre></div>
</div>
<p>Now we create the structs necessary to implement the ufuncs. The typedefs <em>must</em> be made as the ufunc generators take these typedefs as inputs and return an error otherwise</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="k">struct</span> <span class="n">UnarySquare</span>
<span class="p">{</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">argument_type</span><span class="p">;</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">result_type</span><span class="p">;</span>

  <span class="kt">double</span> <span class="nf">operator</span><span class="p">()(</span><span class="kt">double</span> <span class="n">r</span><span class="p">)</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="n">r</span> <span class="o">*</span> <span class="n">r</span><span class="p">;}</span>
<span class="p">};</span>

<span class="k">struct</span> <span class="n">BinarySquare</span>
<span class="p">{</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">first_argument_type</span><span class="p">;</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">second_argument_type</span><span class="p">;</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">result_type</span><span class="p">;</span>

  <span class="kt">double</span> <span class="nf">operator</span><span class="p">()(</span><span class="kt">double</span> <span class="n">a</span><span class="p">,</span><span class="kt">double</span> <span class="n">b</span><span class="p">)</span> <span class="k">const</span> <span class="p">{</span> <span class="k">return</span> <span class="p">(</span><span class="n">a</span><span class="o">*</span><span class="n">a</span> <span class="o">+</span> <span class="n">b</span><span class="o">*</span><span class="n">b</span><span class="p">)</span> <span class="p">;</span> <span class="p">}</span>
<span class="p">};</span>
</pre></div>
</div>
<p>Initialise the Python runtime and the numpy module</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">argv</span><span class="p">)</span>
<span class="p">{</span>
  <span class="n">Py_Initialize</span><span class="p">();</span>
  <span class="n">np</span><span class="o">::</span><span class="n">initialize</span><span class="p">();</span>
</pre></div>
</div>
<p>Now expose the struct UnarySquare to Python as a class, and let ud be the class object.</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">object</span> <span class="n">ud</span> <span class="o">=</span> <span class="n">p</span><span class="o">::</span><span class="n">class_</span><span class="o">&lt;</span><span class="n">UnarySquare</span><span class="p">,</span> <span class="n">boost</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">UnarySquare</span><span class="o">&gt;</span> <span class="o">&gt;</span><span class="p">(</span><span class="s">&quot;UnarySquare&quot;</span><span class="p">);</span>
<span class="n">ud</span><span class="p">.</span><span class="n">def</span><span class="p">(</span><span class="s">&quot;__call__&quot;</span><span class="p">,</span> <span class="n">np</span><span class="o">::</span><span class="n">unary_ufunc</span><span class="o">&lt;</span><span class="n">UnarySquare</span><span class="o">&gt;::</span><span class="n">make</span><span class="p">());</span>
</pre></div>
</div>
<p>Let inst be an instance of the class ud</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">object</span> <span class="n">inst</span> <span class="o">=</span> <span class="n">ud</span><span class="p">();</span>
</pre></div>
</div>
<p>Use the &#8220;__call__&#8221; method to call the overloaded () operator and print the value</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Square of unary scalar 1.0 is &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">inst</span><span class="p">.</span><span class="n">attr</span><span class="p">(</span><span class="s">&quot;__call__&quot;</span><span class="p">)(</span><span class="mf">1.0</span><span class="p">)))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>Create an array in C++</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="kt">int</span> <span class="n">arr</span><span class="p">[]</span> <span class="o">=</span> <span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">}</span> <span class="p">;</span>
</pre></div>
</div>
<p>..and use it to create the ndarray in Python</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">np</span><span class="o">::</span><span class="n">ndarray</span> <span class="n">demo_array</span> <span class="o">=</span> <span class="n">np</span><span class="o">::</span><span class="n">from_data</span><span class="p">(</span><span class="n">arr</span><span class="p">,</span> <span class="n">np</span><span class="o">::</span><span class="n">dtype</span><span class="o">::</span><span class="n">get_builtin</span><span class="o">&lt;</span><span class="kt">int</span><span class="o">&gt;</span><span class="p">(),</span>
                                       <span class="n">p</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">4</span><span class="p">),</span>
                                       <span class="n">p</span><span class="o">::</span><span class="n">make_tuple</span><span class="p">(</span><span class="mi">4</span><span class="p">),</span>
                                       <span class="n">p</span><span class="o">::</span><span class="n">object</span><span class="p">());</span>
</pre></div>
</div>
<p>Print out the demo array</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Demo array is &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">demo_array</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>Call the &#8220;__call__&#8221; method to perform the operation and assign the value to result_array</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">object</span> <span class="n">result_array</span> <span class="o">=</span> <span class="n">inst</span><span class="p">.</span><span class="n">attr</span><span class="p">(</span><span class="s">&quot;__call__&quot;</span><span class="p">)(</span><span class="n">demo_array</span><span class="p">);</span>
</pre></div>
</div>
<p>Print the resultant array</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Square of demo array is &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">result_array</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>Lets try the same with a list</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">p</span><span class="o">::</span><span class="n">list</span> <span class="n">li</span><span class="p">;</span>
<span class="n">li</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="mi">3</span><span class="p">);</span>
<span class="n">li</span><span class="p">.</span><span class="n">append</span><span class="p">(</span><span class="mi">7</span><span class="p">);</span>
</pre></div>
</div>
<p>Print out the demo list</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Demo list is &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">li</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>Call the ufunc for the list</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">result_array</span> <span class="o">=</span> <span class="n">inst</span><span class="p">.</span><span class="n">attr</span><span class="p">(</span><span class="s">&quot;__call__&quot;</span><span class="p">)(</span><span class="n">li</span><span class="p">);</span>
</pre></div>
</div>
<p>And print the list out</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Square of demo list is &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">result_array</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>Now lets try Binary ufuncs. Again, expose the struct BinarySquare to Python as a class, and let ud be the class object</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">ud</span> <span class="o">=</span> <span class="n">p</span><span class="o">::</span><span class="n">class_</span><span class="o">&lt;</span><span class="n">BinarySquare</span><span class="p">,</span> <span class="n">boost</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">BinarySquare</span><span class="o">&gt;</span> <span class="o">&gt;</span><span class="p">(</span><span class="s">&quot;BinarySquare&quot;</span><span class="p">);</span>
<span class="n">ud</span><span class="p">.</span><span class="n">def</span><span class="p">(</span><span class="s">&quot;__call__&quot;</span><span class="p">,</span> <span class="n">np</span><span class="o">::</span><span class="n">binary_ufunc</span><span class="o">&lt;</span><span class="n">BinarySquare</span><span class="o">&gt;::</span><span class="n">make</span><span class="p">());</span>
</pre></div>
</div>
<p>And initialise ud</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">inst</span> <span class="o">=</span> <span class="n">ud</span><span class="p">();</span>
</pre></div>
</div>
<p>Print the two input lists</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;The two input list for binary ufunc are &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span>
          <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">demo_array</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span>
          <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">demo_array</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
</pre></div>
</div>
<p>Call the binary ufunc taking demo_array as both inputs</p>
<div class="highlight-c++"><div class="highlight"><pre><span class="n">result_array</span> <span class="o">=</span> <span class="n">inst</span><span class="p">.</span><span class="n">attr</span><span class="p">(</span><span class="s">&quot;__call__&quot;</span><span class="p">)(</span><span class="n">demo_array</span><span class="p">,</span><span class="n">demo_array</span><span class="p">);</span>
</pre></div>
</div>
<p>And print the output</p>
<div class="highlight-c++"><div class="highlight"><pre>  <span class="n">std</span><span class="o">::</span><span class="n">cout</span> <span class="o">&lt;&lt;</span> <span class="s">&quot;Square of list with binary ufunc is &quot;</span> <span class="o">&lt;&lt;</span> <span class="n">p</span><span class="o">::</span><span class="n">extract</span><span class="o">&lt;</span><span class="kt">char</span> <span class="k">const</span> <span class="o">*&gt;</span><span class="p">(</span><span class="n">p</span><span class="o">::</span><span class="n">str</span><span class="p">(</span><span class="n">result_array</span><span class="p">))</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
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